1. Field of the Invention
The present invention relates to a method of producing a spiral wound gasket for sealing fluid such as liquid including water and oil, and a gaseous body including vapor and gas.
Also, the present invention relates to a device for producing the spiral wound gasket.
2. Description of the Prior Art
In a joint portion of each laying pipe employed under a high temperature and a high pressure condition, a gasket is disposed between a pair of flanges, each flange is fastened by a bolt, and the gasket is closely fitted in each flange, thereby preventing a fluid flowing inside the pipe from leaking to the outside.
For the gasket, a spiral wound gasket is usually employed. As shown in FIGS. 9 and 10, the spiral wound gasket has a structure wherein a filler material 92 made of an asbestos paper, an expanded graphite tape, a 4-fluorinated ethylene resin tape, or the like is stuck on a hoop material 91 made of a long and thin stainless plate having a wave shaped or chevron shaped section so that they may be wound in a spiral state.
A general method of producing this spiral wound gasket is described below.
First, as shown in FIG. 11, the tip portion of the hoop material 91 is folded and inserted in a checking groove 93a of the outer periphery of a core drum 93, whereby the hoop material 91 is stopped by connecting it to the core drum 93. In this state, the core drum 93 is rotated so that only the hoop material 91 is wound around the outer periphery of the core drum 93 at least once. Then, the filler material 92 is stuck on the hoop material 91 so as to be wound in a spiral state. Thereafter, only the hoop material 91 is further wound two or three times. Moreover, the hoop material 91 and the filler material 92 wound 16 in a spiral state are removed from the core drum 93, thereby cutting off the folded area on the tip portion of the hoop material 91, which is inserted in the checking groove 93a of the core drum 93.
An initial portion of the hoop material 91 to be wound is fixed in a predetermined zone of the hoop material 91 by spot welding or the like. A last portion of the hoop material 91 to be wound is fixed in a predetermined zone of the preceding-round of the wound hoop material 91 by the welding spot or the like.
However, the conventional producing method mentioned above requires that the hoop material 91 and the filler material 92 wound in a spiral state are removed from the core drum 93, before positioning a step for cutting off the tip portion of the hoop material 91 inserted in the checking groove 93a of the core drum 93. Consequently, the number of steps is increased, and it is required to manually perform a cutting operation, thereby incurring an expensive production cost. Moreover, the cut-off portion of the hoop material 91 has to be wasted, which results in a problem wherein a yield of the hoop material 91 is worse.
In order to overcome the above problems, a method shown in FIG. 12 is proposed as below. A pressing force is applied to the tip portion of the hoop material 91, thereby forming a flat portion 91a. A checking hole 91b is formed on the flat portion 91a by piercing the hoop material. On the other hand, the core drum 93 is provided with a checking pin 94 whose tip can protrude or retract elastically from the outer periphery of the core drum 93. The checking pin 94 catches the checking hole 91b of the hoop material 91, thus permitting winding the hoop material 91 around the core drum 93. (See the gazette of Japanese Patent Publication No. H8-33180.)
According to the method, the step of cutting off the tip portion of the hoop material 91 is not required. However, it is required to form the flat portion 91a for providing the checking hole 91b by a step of applying pressure or the like to the tip portion. A width of the tip portion after forming the flat portion 91a, is greater than the reminder of the portion thereof, whereby local unevenness is generated on the sealing surface of the completed gasket owing to a shape of the tip portion thereof. As a result, there is a fear wherein the unevenness adversely affects the sealing property.
Furthermore, a great gap is generated between the flat portion 91a and the chevron portions 91c, 91c of a second-round hoop material 91 wound around the outer periphery thereof, whereby welding the flat portion 91a to the hoop material 91 on the outer periphery thereof is not ensured, thereby, in some cases, causing a problem wherein it is easy to separate the flat portion 91a therefrom.
In addition, though the second-round hoop material 91 directly wound around the outer periphery thereof unforcedly presses the checking pin 94 to move downwardly, the operation of winding the first-round hoop material 91 is not fully completed at the time when the checking pin 94 is pressed to move downwardly. Moreover, the hoop material 91 is intensively drawn, thereby increasing the contact pressure between the checking pin 94 and the checking hole 91b. In some cases, the unforced friction between the tip portion thereof and the checking hole 91b greatly damages the tip portion of the checking pin 94, when the checking pin 94 is pressed to move downwardly, with the result that there are problems wherein the durability of the device is bad and the operation of replacing the checking pin 94 is required.